Electronic circuit parts that are attached to circuit boards during use, such as PGA's, IC devices, electrical connectors, switches and the like (hereafter referred to collectively as "electronic devices") have numerous terminals or pins. Such pins are connected to conductive pads or conductive paths of circuit boards during use.
In the case of such electronic devices, the number of pins has increased and the pins have been installed at a higher density (smaller pitch), as the size of electronic equipment has been reduced and the performance of such equipment has been improved. Soldering is a common technique used to effect electrical connection of such numerous high-density pins to circuit boards. In the case of high-density pins, however, not only is soldering difficult but a drop in reliability caused by solder bridges or the like also becomes a problem. Furthermore, it is extremely difficult to remove electronic devices once these devices have been soldered. Accordingly, such soldered devices are difficult to maintain and service.
In order to overcome the drawbacks of soldering such as these, direct electrical connections achieved by press-fitting pins into circuit boards that have plated through-holes have been proposed. Such techniques have spread widely, especially in the field of communications equipment.
A compliant pin terminal known as the ACTION PIN.RTM. terminal has been commercially marketed by AMP Incorporated as one type of such press-fit connecting pin. This compliant pin is constructed so that portions of the shaft of the pin are sheared in the axial direction and mutually offset along the shear surfaces, as disclosed, for example, in U.S. Pat. No. 4,186,982. Accordingly, this pin can be press-fitted relatively smoothly against the inside walls of plate through-holes, so that highly reliable electrical connections can be achieved and maintained with a large contact pressure and without damaging the plating layer. A similar compliant pin is also disclosed in Japanese Utility Model Application Kokai No. 58-14683, and a pin split into three parts is disclosed in Japanese Utility Model Application Kokai No. 60-45463 and elsewhere.
On the other hand, compliant pins or press-fit pins that have been given a deformable cross-sectional shape by applying pressure or mechanical working without shearing the shaft portion of the pin are disclosed in Japanese Patent Publication No. 62-5575, Japanese Utility Model Publication No. 58-154572, Japanese Utility Model Publication No. 60-172370, Japanese Utility Model Publication No. 58-157974, Japanese Patent No. 58-172881 and elsewhere.
The conventional compliant pins described above are sufficient for certain specified applications but are difficult or impossible to use in the case of small-size high-density pins with extremely slender shafts, such as those having a diameter of approximately 0.4 mm, which are required by recent electronic devices. The reasons for this are as follows:
First, in the case of compliant pins in which the shaft portion is sheared or offset so that the shaft portion is split into two or three parts as described above, such working cannot be applied to fine pins that have a diameter of approximately 0.4 mm. Furthermore, when conventional compliant pins that have been worked so that the cross-sectional shape of the pin is deformable are used in through-holes which have a diameter of approximately 0.4 mm, the amount of deformation is small so that an excessive amount of insertion force is required for press-fitting. As a result, the pins themselves undergo buckling deformation. Furthermore, the plating layers of the through-holes may be destroyed, or, depending on the dimensional working tolerances of the through-holes and pins, it may be impossible to obtain electrical connections of sufficiently high reliability.
U.S. Pat. No. 3,827,004 discloses a press-fit connecting pin including a shaft having deformable strips projecting radially therefrom at separate locations. The locations are angularly positioned with respect to one another and are dimensioned to engage the inside walls of the through-hole when inserted therein. The shaft of the fins is substantially square and includes pairs of collapsible pins that bend toward each other when the pin is inserted into a through-hole.